1. Field
Embodiments described herein relate to array antennas and in particular to active electronically scanned array antennas.
2. Description of Related Art
An active electronically scanned array (AESA) antenna is an antenna comprising multiple radiators, or elements, the relative amplitude and phase of which can be controlled, making it possible to steer the transmit or receive beam without moving the antenna. Such an antenna includes an aperture for transmitting or receiving waves traveling in free space, and it may include back-end circuitry, including electronics modules for generating signals to be transmitted and for processing received signals. Each element within the aperture may incorporate, or be connected to, a circulator, which separates the signals corresponding to transmit and receive channels, and which is connected to a transmit channel and a receive channel in the back-end electronics. The circulator may be fabricated as a microstrip circuit on a ferrite substrate, with a permanent magnet secured on or near the signal side of the substrate, and with a magnetic material, i.e., a material with a high magnetic permeability, on the ground plane side of the substrate to shape the magnetic field produced by the permanent magnet.
Prior art aperture structures include notch radiator arrays of the type described in U.S. Pat. No. 6,600,453, assembled from long, flat “sticks,” or “slats,” each including a series of notch radiators. In such an embodiment, a certain minimum notch depth may be required to achieve acceptable bandwidth, and the circulators may be installed in the plane of the sticks, resulting in a relatively deep aperture.
Another prior art aperture structure is disclosed in U.S. Pat. No. 7,315,288. This structure includes long slots spanning multiple array elements, periodically driven along their lengths. Probes in the form of current loops, located at intervals along each slot, excite the long slot. The probes, which are balanced transmission line or feed structures, are connected to single-ended transmit and receive electronics through baluns. In such a structure the baluns may be behind the radiators, and the circulators behind the baluns, and this combination may increase the depth of the antenna. Moreover the baluns may be a cause of electrical loss.
Especially in space-constrained applications such as in aircraft, it may be important to reduce the thickness and, thereby, the volume of an array antenna; moreover it is desirable to produce the antenna at a modest cost. Thus, there is a need for a low-cost, low-profile AESA antenna.